The attachment of useful materials such as catalysts, reagents, chelating or complexing agents, and proteins to insoluble supports is well-known. With the attending advantages of ease of removal and recovery from the system, e.g., by simple filtration, regeneration (if necessary), and recycling coupled with the increased utilization of continuous flow systems in both general chemical processing and diagnostic monitoring procedures, supported materials are ubiquitous in today's technology. One indication of this is the listing of "Polymer- Supported Reagents" as a separate heading in the General Subjects Index of Chemical Abstracts beginning in 1982.
Concerning the nature of the insoluble support material, both inorganic polymers (notably silica gel and alumina) and organic polymers have been utilized. Factors, however, such as increased capacity because of better porosity (especially with the so-called "gel-type" polymers which swell somewhat and allow relatively free access by solvent and solute to the bound functionality within the support) and better control of the polar nature of the support (by selection of appropriate comonomers), which has been shown to directly affect reaction rate, have led to a general preference for the organic polymer supports. Polystyrene has been the solid support material most extensively utilized.
The attaching functionality for polystyrene supports most often utilized has been the chloromethylphenyl group. These reactive, solid supports are the so-called "Merrifield resins", so named for R. B. Merrifield (J. Am. Chem. Soc., 85, 2149 (1963)) who received the Nobel Prize in Chemistry in 1984 for these and other achievements. Merrifield resins are extremely useful for conducting solid phase peptide syntheses, but their broad utilization as reactive, solid supports is limited because of the relative nonpolarity of the hydrophobic polystyrene backbone, an oftentimes unpredictable attaching reaction which involves nucleophilic displacement of chloride ion, and a relatively low capacity of reactable chloromethylphenyl groups per gram of polymer. The chloromethylphenyl and other reactive functionalities are discussed by N. K. Mathur, C. K. Narang, and R. E. Williams, "Polymers as Aids in Organic Chemistry", Chapter 2, Academic Press: New York (1980).
The present state of reactive, insoluble supports may be summarized by the statement that no one support is broadly suitable for the many applications of solid-supported materials. The spectrum of properties required varies tremendously depending on the end-use, which includes such diverse applications as mediating organic synthetic transformations, removing precious metals from sea water or heavy metal contaminants from industrial effluants, utilizing supported metals as catalysts for conducting organic reactions and polymerizations, resolving optical isomers, separating biomacromolecules, and attaching biomacromolecules.
Azlactones have not been previously utilized as attaching groups on insoluble supports. Azlactones have, however, been proposed to be useful in two instances.
U.S. Pat. No. 4,070,348 teaches the preparation of water-swellable, crosslinked bead copolymers having 0.2 to 5 mol percent crosslinking monomer and at least 10 mole percent of a water soluble comonomer incorporated therein. The copolymers are reactive with proteins primarily by the inclusion of oxirane groups which are the only reactive groups claimed. Several "activated carboxyl groups" (col. 4; line 42), however, are listed including a 2-alkenyl azlactone, 2-isopropenyl-4,4-dimethyl-oxazolone-5 (col. 5; lines 2-3), and reaction of this compound with a primary amino group of a protein is depicted schematically (col. 5; lines 6-14). No additional information or enabling disclosure is given about incorporation of the azlactone into a hydrophilic, crosslinked bead copolymer or reaction of an azlactone-functional insoluble support with a protein or any other functional material. The crosslinked, bead copolymers of U.S. Pat. No. 4,070,348 are all prepared purposely in essentially an anhydrous condition, i.e. with care being taken to exclude water.
L. D. Taylor, et al., Makromol. Chem., Rapid Commun., 3, 779 (1982) have proposed azlactones to be useful as reactive groups on polymeric supports. Only the bulk homopolymerization of 2-vinyl-4,4-dimethylazlactone to form a polymeric "plug" is described. No mention of crosslinking and generation of polymeric beads is given. Furthermore, described at some length is the susceptibility of the poly(azlactone) to hydrolysis, i.e., ring-opening reaction with water [equation (1)]. Hydrolysis is regarded as being very facile, occurring even with traces of moisture often present in organic solvents for the homopolymer, as follows: ##STR2## Based on this account of the propensity toward hydrolysis, it is entirely unexpected that an azlactone-functional support could be selectively reacted with a functional material in aqueous media.